Showing papers on "Inconel published in 2018"

Effects of Selective Laser Melting additive manufacturing parameters of Inconel 718 on porosity, microstructure and mechanical properties

Abstract: The effect of SLM parameters on porosity, microstructure and mechanical properties is studied. To this purpose, the Selective Laser Melting (SLM) technology is applied to manufacture Inconel 718 specimens. The material, the manufacturing process, the Hot Isostatic Pressure (HIP), heat treatment, observation procedures and characterisation of mechanical properties are presented. A columnar-dendritic microstructure was observed on all the SLM specimens and a Volumetric Energy Density (VED) effect on the latter was also noted. The rate of porosity varies in relation to the VED and is considerably reduced after HIP. The heat treatment erases the dendritic microstructure, significantly enhances microhardness and confers on the alloy tensile mechanical properties comparable to forged Inconel 718.

Effects of nano-cutting fluids on tool performance and chip morphology during machining Inconel 718

Abstract: Flood cooling is a typical cooling strategy used in industry to dissipate the high temperature generated during machining of Inconel 718. The use of flood coolant has risen environmental and health concerns which call for different alternatives. Minimum quaintly lubricant (MQL) has been successfully introduced as an acceptable coolant strategy; however, its potential to dissipate heat is much lower than the one achieved using flood coolant. MQL-nano-cutting fluid is one of the suggested techniques to further improve the performance of MQL particularly when machining difficult-to-cut materials. The main objective of this study is to investigate the effects of two types of nano-cutting fluids on tool performance and chip morphology during turning of Inconel 718. Multi-walled carbon nanotubes (MWCNTs) and aluminum oxide (Al2O3) gamma nanoparticles have been utilized as nano-additives. The novelty here lies on enhancing the MQL heat capacity using different nano-additives-based fluids in order to improve Inconel 718 machinability. In this investigation, both nano-fluids showed better results compared to the tests performed without any nano-additives. Significant changes in modes of tool wear and improvement in the intensity of wear progression have been observed when using nano-fluids. Also, the collected chips have been analyzed to understand the effects of adding nano-additives on the chip morphology. Finally, it has been found that MWCNT nano-fluid has shown better performance than Al2O3 nano-fluid.

Additive manufacturing of Inconel 718—Copper alloy bimetallic structure using laser engineered net shaping (LENS™)

Abstract: To understand processing ability and measure resultant interfacial and thermal properties of Inconel 718 and copper alloy GRCop-84, bimetallic structures were fabricated using laser engineering net shaping (LENS™), a commercially available additive manufacturing technique. It was hypothesized that additively combining the two aerospace alloys would form a unique bimetallic structure with improved thermophysical properties compared to the Inconel 718 alloy. Two approaches were used: the direct deposition of GRCop-84 on Inconel 718 and the compositional gradation of the two alloys. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray Diffraction (XRD), Vickers microhardness and flash thermal diffusivity were used to characterize these bimetallic structures to validate our hypothesis. The compositional gradation approach showed a gradual transition of Inconel 718 and GRCop-84 elements at the interface, which was also reflected in the cross-sectional hardness profile across the bimetallic interface. SEM images showed columnar grain structures at the interfaces with Cr2Nb precipitate accumulation along grain boundaries and the substrate-deposit interface. The average thermal diffusivity of the bimetallic structure was measured at 11.33 mm2/s for the temperature range of 50 °C–300 °C; a 250% increase in diffusivity when compared to the pure Inconel 718 alloy at 3.20 mm2/s. Conductivity of the bimetallic structures increased by almost 300% compared to Inconel 718 as well. Such structures with designed compositional gradation and tailored thermal properties opens up the possibilities of multi-material metal additive manufacturing for next generation of aerospace structures.

Comparison of microstructures and mechanical properties of Inconel 718 alloy processed by selective laser melting and casting

Abstract: The paper comparatively investigates the microstructures and mechanical properties of Inconel 718 superalloy manufactured by selective laser melting (SLM) and casting. The finite element analysis (FEA) method is used to simulate the temperature fields during SLM and casting processes. Driven by ultra-high temperature gradient and ultra-fast cooling rate during SLM process, the fine grains (average grain size of 48 µm) and dispersed fine precipitation in SLM-ed sample even after HSA (homogenization + solution + aging) and HA (homogenization + aging) heat treatment significantly enhance its mechanical properties, which far exceeds that of casting with average grain size of 1300 µm, and is comparable to that of forging. The microstructure of casting with coarse irregular Laves phases, acicular δ precipitates and globular carbides in the interdendritic zones after HSA heat treatment and some defects existed possibly result in premature failure of tensile samples. The microstructure without δ phases but only some globular carbides in the grain boundary of SLM-ed sample after HA heat treatment possesses higher mechanical properties than that after HSA heat treatment, in which there is only some finer needle-like δ phase and few carbides are precipitated in the grain boundaries. The analysis shows the large amounts of δ phase precipitated in the matrix will deteriorate the plasticity of SLM-ed IN718 superalloy, the appropriate reduction of the δ phase will improve the strength and plasticity of material simultaneously.

Thermal conductivity of metal powders for powder bed additive manufacturing

Abstract: The thermal conductivities of five metal powders for powder bed additive manufacturing (Inconel 718, 17-4 stainless steel, Inconel 625, Ti-6Al-4V, and 316L stainless steel) were measured using the transient hot wire method. These measurements were conducted with three infiltrating gases (argon, nitrogen, and helium) within a temperature range of 295–470 K and a gas pressure range of 1.4–101 kPa. The measurements of thermal conductivity indicate that the pressure and the composition of the gas have a significant influence on the effective thermal conductivity of the powder, but that the metal powder properties and temperature do not. Our measurements improve the accuracy upon which laser parameters can be optimized in order to improve thermal control of powder beds in selective laser melting processes, especially in overhanging and cellular geometries where heat dissipation by the powder is critical.

Additive manufacturing of Inconel 718 – Ti6Al4V bimetallic structures

Abstract: Bimetallic structures belong to a class of multi-material structures, and they potentially offer unique solutions to many engineering problems. In this work, bimetallic structures of Inconel 718 and Ti6Al4V (Ti64) alloys were processed using laser engineered net shaping (LENS™). During LENS™ processing, three build strategies were attempted: direct deposition, compositional gradation and use of an intermediate bond layer. Inconel 718 and Ti64 alloys exhibit thermal properties mismatch along with brittle intermetallic phase formation at the interface resulting in delamination. For a successful build, the use of a compositional bond layer (CBL) was employed, which was a mixture of a third material - Vanadium Carbide - with the parent alloys to form an intermediate layer used in bonding the two immiscible alloys. A crack-free bimetallic structure of Inconel 718 and Ti64 was demonstrated. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction and Vickers hardness were used to characterize these bimetallic structures. XRD analysis indicated presence of Cr3C2 phases. CBL improved the bonding strength by avoiding formation of brittle intermetallic phases such as TiNi3 and Ti2Ni as well as reducing thermal stresses at the interface. Our results successfully demonstrate the formation of Inconel 718 and Ti64 bimetallic structures using a laser-based commercially available additive manufacturing approach.

Effect of heat treatment variations on the mechanical properties of Inconel 718 selective laser melted specimens

Abstract: The wide usage of Inconel 718 alloy is based on its fusion weldability and its availability in many different forms including cast, wrought and powder. Thus with the emergence of additive manufacturing (AM) techniques for metals, Inconel 718 is a prime candidate for materials to be considered. Powders that have been developed for powder metallurgy are readily available for use in various AM processes such as selected laser melting (SLM) powder bed. While much research has focused on optimizing the deposition parameters to achieve fully densified specimens, subsequent heat treatments and their effect on the microstructure also need to be understood. This study evaluated the microstructure of SLM specimens of Inconel 718 after various heat treatments and compared the resulting effect on the quasi-static mechanical properties.

Residual stress evaluation in selective-laser-melting additively manufactured titanium (Ti-6Al-4V) and inconel 718 using the contour method and numerical simulation

Abstract: Residual stresses play an important role for the structural integrity of engineering components. In this study residual stresses were determined in titanium alloy (Ti-6Al-4V) and Inconel 718 samples produced using selective-laser-melting (SLM) additive manufacturing. The contour method and a numerical simulation approach (inherent-strain-based method) were used to determine the residual stress distributions. The inherent-strain-based method reduces the computational time compared to weakly-coupled thermo-mechanical simulations. Results showed the presence of high tensile residual stresses at and near the surface of both titanium and Inconel alloys samples, whereas compressive residual stresses were seen at the center region. A good agreement was seen between the results obtained from contour method and the numerical simulation, particularly 1 mm below the surface of the samples.

Influence of process parameters and heat treatments on the microstructures and dynamic mechanical behaviors of Inconel 718 superalloy manufactured by laser metal deposition

Abstract: To achieve high-performance nickel-based superalloys by laser metal deposition (LMD) technology for applications in aeroengines, we prepared Inconel 718 superalloys by LMD with three groups of process parameters and then heat treated them by two different protocols. We carried out compressive experiments for these Inconel 718 samples over a wide range of strain rate (0.001–5000/s) to evaluate the effects of process parameters and heat treatments on their microstructures and dynamic mechanical properties. We observed both the initial microstructures and the failure characteristics of the samples using the optical microscope and the scanning electron microscope. We found that a higher energy input density during laser additive manufacturing led to a wider range of primary dendrite spacing. The plastic flow stress of the alloy decreased near-linearly with increase in primary dendrite spacing. The anisotropy of the compressive properties of the sample resulted from the anisotropy of the as-deposited and the direct aged structures, while the microstructural and mechanical anisotropy almost vanished after full heat treatment. We further carried out compressive experiments over a wide range of strain rate (0.001–5300/s) and temperature (298–1193 K) to understand the mechanical properties of Inconel 718 by LMD in an extremely high-strain rate and high-temperature loading environment. We noticed an anomalous high-temperature peak in the flow stress, in the flow stress vs. temperature relation, under different strain rates, and we proved that it is attributed to the third type of strain aging effect. Finally, by observing the compressive failure characteristics, we found that the propagation path of a crack is dependent on the loading direction. The compressive fractography morphology could reflect the effect of heat treatment on the ductility of the samples. Furthermore, it was evident that the initial defects (gas and shrinkage porosities) in Inconel 718 samples caused by LMD can contribute to the generation, deflection, and branching of cracks.

Microstructure and performance evolution and underlying thermal mechanisms of Ni-based parts fabricated by selective laser melting

Abstract: This work presented a comprehensive study of microstructural evolution, microhardness and quantitative thermodynamic analysis within the molten pool during Selective Laser Melting (SLM) of Inconel 718 parts. Microstructures and corresponding microhardness of different zones within the molten pool experienced the following evolution: fine cellular dendrites or equiaxed grains on the top surface (387HV); columnar dendrites with single direction of grain growth at the bottom (337HV); columnar dendrites with multiple directions of grain growth at the edge of the molten pool (340HV-350HV); microstructures between cellular and columnar grains around the center of the molten pool (363HV). The impact of Gaussian-distributed laser energy and relatively weak thermal conductivity and convection of Inconel 718 contributed to the variation of temperature gradient at different zones within the molten pool. The formation of different kinds of microstructures in the molten pool was controlled by the temperature gradient (which determined the direction of grain growth) and the cooling rate (which determined the size of grain growth). The variation of microhardness within the molten pool was ascribed to the number of grain boundaries and the stress characteristics of different kinds of microstructures under mechanical load. The zones with fine cellular grains had elevated mechanical performance due to the superior capability to endure the load. This work hopefully provides scientific and theoretical support for SLM-processed Inconel 718 parts with favorable properties.

Effect of laser focus shift on surface quality and density of Inconel 718 parts produced via selective laser melting

Abstract: Selective laser melting (SLM) is a method of laser powder bed fusion additive manufacturing (AM) currently being pursued in numerous industries, including space launch and space flight. In this study we performed an extensive parameter development investigation to better understand the effect of laser parameters on surface roughness, density, and porosity of SLM Inconel 718 parts. Laser energy density was varied via laser focus shift, and the effects on porosity in both as-printed and post-HIP treated states were analyzed. Tensile testing was also conducted to investigate the effect of processing conditions on the mechanical properties of SLM 718. It was found that for these laser parameters, while the material met ultimate tensile strength and yield strength requirements per AMS 5662, the strain-to-failure was reduced with negative focus shift due to increases in porosity levels. It was also found that while correlations were observed between surface roughness, density, and porosity within the laser focus shift range investigated, porosity measurement appears to be the clearest indicator of build quality for AM processed 718.

Microstructure investigation of Inconel 625 coating obtained by laser cladding and TIG cladding methods

Abstract: The purpose of this study was to investigate the microstructure of the Ni base Inconel 625 coatings that were fabricated on the Inconel 738 substrate with two processes of laser cladding and TIG cladding For this purpose, single-pass samples were precipitated to obtain optimal parameters In the laser cladding method, laser power, laser scanning rate and powder feed rate were considered as variables, and current and its type were considered as variables for the TIG method Based on the results, using the parameters of optimum single-pass samples that were free of porosity, crack and had minor geometric dilution, coatings were applied in both methods with 50% overlap In order to microstructural, elemental and phasic characterization, field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were used Based on the results, the microstructure of coatings from surface to interface of coating/substrate consists of coaxial, columnar and cellular structure dendrites, respectively, and the laser coating has a finer microstructure due to the higher cooling rate In addition, the austenite, carbide and Laves phases were observed in both coatings

Towards Sustainable Machining of Inconel 718 Using Nano-Fluid Minimum Quantity Lubrication

Abstract: Difficult-to-cut materials have been widely employed in many engineering applications, including automotive and aeronautical designs because of their effective properties. However, other characteristics; for example, high hardness and low thermal conductivity has negatively affected the induced surface quality and tool life, and consequently the overall machinability of such materials. Inconel 718, is widely used in many industries including aerospace; however, the high temperature generated during machining is negatively affecting its machinability. Flood cooling is a commonly used remedy to improve machinability problems; however, government regulation has called for further alternatives to reduce the environmental and health impacts of flood cooling. This work aimed to investigate the influence of dispersed multi-wall carbon nanotubes (MWCNTs) and aluminum oxide (Al2O3) gamma nanoparticles, on enhancing the minimum quantity lubrication (MQL) technique cooling and lubrication capabilities during turning of Inconel 718. Machining tests were conducted, the generated surfaces were examined, and the energy consumption data were recorded. The study was conducted under different design variables including cutting speed, percentage of added nano-additives (wt.%), and feed velocity. The study revealed that the nano-fluids usage, generally improved the machining performance when cutting Inconel 718. In addition, it was shown that the nanotubes additives provided better improvements than Al2O3 nanoparticles.

Hot tensile behavior of cold-rolled Inconel 718 alloy at 650 °C: The role of δ phase

Abstract: Cold-worked Inconel 718 alloy has successful applications in turbine engines due to its elevated strength. Otherwise, cold working will bring about the undesired ductility degradation accompanied with strength improving. Meanwhile, the susceptibility to δ precipitation is increased with modified morphology. To address these issues, this work aims expressing the effect of cold-rolling on hot ductility and the role of δ phase regarding differential morphologies in tensile behavior of Inconel 718 alloy at 650 °C. The results revealed that the ductility degradation can be attributed to the interactions of necking, microstructure instability and oxidation process tailored by cold-rolling. Nevertheless, appropriate cold-rolling is proved to enhance the resistance to crack propagation. The needlelike δ phase in strain-free structure tightly hindered the migration of horizontal GBs to enhance the strength but promote the intergranular brittle cracking, resulting in the degradation of ductility. In contrast, the δ phase with modified granular morphology in cold-rolled structures showed good deformation compatibility with horizontal GBs, playing a positive role in delaying necking occurrence and impeding crack propagation. In summary, the granular δ precipitation endowed cold-rolled Inconel 718 alloy with a superior combination of strength and ductility at 650 °C.